An exploration of post-transplantation gamma-delta T cell phenotype and function.

Last year, over 100,000 people worldwide received a life-saving organ transplant. Transplantation can cure both adults and children of fatal diseases, restore their independence, and improve their quality of life. The success of transplantation -- traditionally measured as whether someone is alive at one or five years after their operation -- is impressive. At last count, 99% of people receiving a kidney transplant were alive after a year, and 97% were alive after five. From this it is tempting to conclude that no further work is required. However, these numbers only present part of the picture, and particularly for children five additional years is not a good measure of success. If we widen our measure to ten years, the numbers are more sobering: for every ten children receiving a kidney transplant three will have died, and for every ten children receiving a liver transplant seven will have died.

The major causes of death following transplantation are related to the powerful medications required to prevent transplant rejection. These medications work by switching off the entire immune system. They have significant side effects, rendering people more vulnerable to infection and increasing their risk of developing cancer and heart disease. An in depth understanding of how our immune system responds to transplants is important to develop safer, more targeted therapies.

My research will explore the role of a rarely studied white blood cell, termed a gamma-delta T cell, in transplantation. This cell has unique characteristics that set it apart from other cells in the immune system and it plays an important role following transplantation. For example, a proportion of patients who receive liver transplants can be taken off immunosuppressive medications without rejecting their transplant. This is termed operational tolerance. If we analyse blood samples from these operationally tolerant patients, we see an increased number of a gamma-delta T cell subtype. We observe a similar phenomenon in pregnant women, a biological analogy to receiving a transplant. In women who have a successful pregnancy, we see an increase in the same gamma-delta T cell subtype seen in operationally tolerant liver transplant patients. Conversely, in pregnancies that are lost the same increase in the gamma-delta T cells is missing.

I will investigate the function of these white blood cells to better define how they respond to 'foreign' cells and to examine how they contribute to the desirable clinical outcomes described above. My research is important for several reasons. On a scientific level, there remain numerous crucial yet unanswered questions about gamma-delta T cells that have the potential to significantly deepen our understanding of the human immune system. From a clinical perspective, there is the tantalising prospect of harnessing these cells therapeutically for patients receiving transplants as an 'off-the-shelf' product.

Over the course of my Clinical Research Training Fellowship I will work in the Transplantation Research and Immunology Group at the University of Oxford to answer these questions. I will use blood donated by healthy volunteers and transplant recipients to investigate the structure and function of these cells in higher resolution than previously possible using cutting-edge techniques to look at their cellular machinery. I will investigate the signatures of these cells in the peripheral blood of kidney transplant recipients and assess whether this signature can be used to predict the success of immunosuppression withdrawal. I will also investigate whether they can be used to prevent skin transplant rejection in an animal model.

Solid organ transplantation is curative surgery for end-stage organ dysfunction. The immunosuppression required to prevent allorejection, however, causes substantial morbidity and mortality. A granular description of tolerogenic and alloreactive cell populations within the human immune system is necessary to develop targeted immunotherapies. Gamma-delta T cells are a highly conserved lymphocyte subpopulation characterised by innate and adaptive properties. They initiate, propagate, and modulate immune responses, and have been associated with operational tolerance and a reduced cancer risk following renal transplant.

I aim to investigate the gamma-delta T cell compartment in transplantation and identify therapeutic opportunities that capitalise on their unique identity and function. My fellowship comprises three objectives:
1. define the cell surface, transcriptomic, and functional signatures of gamma-delta T cell subsets. This will be achieved using bulkRNAseq and flow cytometry of human blood to identify immunoregulatory signatures.
2. investigate the impact of autologous regulatory T cell therapy on peripheral and infiltrating gamma-delta populations in human renal transplant recipients. I will utilise single cell RNAseq and multiplexed transcriptomic profiling of our unique biobank from renal transplant recipients to probe for tolerising signatures associated with successful immunosuppression withdrawal.
3. assess the efficacy of gamma-delta subsets in preventing skin graft rejection using an in vivo model of transplantation. I will generate data assessing the therapeutic potential of autologous and allogeneic immunoregulatory gamma-delta T cells.

My fellowship proposal is an exciting opportunity to generate insights into unconventional lymphocyte biology and investigate their therapeutic potential for transplant recipients, in addition to a personal opportunity to receive world-class research training in bioinformatics and single cell sequencing.

This research programme will characterise the structure and function of the gamma-delta T cell compartment following renal transplantation in adult recipients. The academic outputs are expected to deepen our knowledge of unconventional lymphocytes, further our understanding of the mechanisms of rejection following transplantation and assess the therapeutic potential of the regulatory subpopulation of gamma-delta T cells. This fellowship will generate diverse academic, societal, and economic impact. Annual reviews of this statement will ensure that opportunities arising throughout the fellowship are fully capitalised on.

Academic impact: There is substantial interest in the structure and function of the unconventional lymphocyte compartment illustrated by the 2019 British Society of Immunology congress who devoted two parallel sessions to non-classical lymphocytes. The research spaces in which gamma-delta T cells are being interrogated are diverse and include basic immunology, oncology, microbiology, and autoimmunity. There is a paucity of study into non-classical lymphocytes following transplantation. Within transplantation science, this fellowship will generate impact through combining novel technologies with unique patient samples. The Transplantation Research and Immunology Group are the only group in the UK running a clinical trial of regulatory cell therapy following renal transplantation (www.bit.ly/TWOStudy). Through this trial the group has access to a bank of unique human samples that can deepen our understanding of unconventional lymphocyte biology, assess their interaction with autologous regulatory T cell therapy, and better characterise immunoregulatory gamma-delta T cells. Through our collaboration with the Willcox laboratory at the University of Birmingham, this proposal is well-positioned to generate detailed functional definitions of gamma-delta T cell biology and deliver insights that will impact diverse intellectual fields.

Societal impact: Clinical Research Training Fellows occupy a privileged platform for delivering societal impact being situated in both academic and clinical spheres. For individual transplant recipients, this proposal will generate impact through deepening our understanding of how the body recognises and rejects transplanted tissue and through identifying novel therapeutic pathways. Reducing the reliance on conventional immunosuppression will reduce the requirement for re-transplantation thereby increasing the pool of available organs and maximising the impact of transplantation on a societal level. More broadly, societal impact in the form of raising the profile of clinical research and inspiring future generations to pursue academic medicine will be generated in this fellowship through outreach and educational events.

Economic impact: There is substantial industry interest in biologic therapeutics, particularly cell therapies. This is evidenced by the recent 67% increase in the number of cell products entering research and development pipelines of large pharmaceutical companies [1]. Cultivating UK based expertise in cellular therapies will enhance our economic competitiveness in this flourishing market. The fellowship proposal occupies the cell therapy space and is well positioned to deliver economic impact through undertaking preliminary studies into a regulatory gamma-delta T cell product and generating insights into how unconventional lymphocytes interact with other cellular products such as regulatory T cell therapy. This programme of work is likely to influence the development of existing and future cell therapy products.

[1] Lloyd, I. (2017) Pharma R&D Annual Review 2017. London, UK: Pharmaproject.